We will continue research in respiratory mechanics in four projects: 1. Micromechanics of the lung. Fine source, low energy X-rays in combination with high resolution film or electronic image processing will be used to obtain visualization of lung at the sub-acinar level. The variability of collateral flow resistance in excised dog lungs will be studied systematically. The gas compression technique for estimating pulmonary tissue hysteresis will be applied to measurements in living humans. 2. Airway aerodynamics. Data inversion techniques with non-negative constraints will be applied to the problem of smoothing flow-volume curves. The newly developed impedance analyzer and fast responding body plethysmograph will be used to study the frequency response characteristcs of the airways. 3. Chest wall mechanics and respiratory control. Continuous measurement of arterial pCO2 will be made on humans exposed to positive pressure breathing in order to assess the importance of chemical factors in the neural responses to changes in operating length of the diaphragm. The role of the separate abdominal muscles in breathing will be assessed in dogs and man with surface and needle electrode electromyography. 4. Development and evaluation of tests of pulmonary function. The influence of gas density, bronchodilitation and brochoconstriction on the reproducible detail of forced expiratory flow-volume curves will be studied in human subjects.